1. Field of Invention
The invention relates to a needle gripper.
2. Description of Related Art
So-called needle grippers are devices with preferably a plurality of gripping needles which can be retracted into and extended from a gripper base part or a gripper housing, for gripping a workpiece. Such needle grippers are used particularly for gripping fabrics, fiber materials, fiber composites and other materials that can be penetrated by needles. Needle grippers are also used particularly for picking up such workpieces in layers from a stack of workpieces and thus for separating them.
The reliability of the needle gripper here depends on a precise and failure-free retracting and extending of the gripping needles. In the process, it can be problematic, on the one hand, when the stroke depth of the gripping needles is not adapted to the properties of the workpieces, particularly to the thickness of the workpiece layer. In this case, a reliable picking up and separation of an individual workpiece layer is not reliably possible. Moreover, in the case of repeated picking up of fiber workpieces, fiber parts are unintentionally pulled into the gripping device, due to the retracting and extending of the gripping needles, which also negatively impacts the reliability and which can require maintenance and cleaning.
From DE 10 2011 010 326 A1 and DE 20 2012 100 849 U1, needle grippers are known, in which the extension and retraction of the gripping needles is driven via a pinion gear by a piston which can be displaced axially and which in particular is driven pneumatically. Here, the stroke of the drive piston is limited by means of a stop acting in axial direction of the piston. A setting of the piston stroke and thus indirectly of the stroke of the retractable and extendable gripping needles here requires a variation of the axial position of the stop for the drive piston.
The problem of the present invention consists, in the case of a needle gripper, in increasing the reliability of the handling of workpieces and at the same time reducing the susceptibility to failure of the needle gripper in operation. Here, in particular, a reliable adaptation of the penetration depth of the gripping needles is to be made possible, and it should be made possible to conveniently do the cleaning and maintenance work that becomes necessary in the case of repeated gripping procedures.